The present invention relates to an image pickup apparatus for obtaining spectral images of an object, and particularly relates to an image pickup unit in a medical endoscope for obtaining spectral images of fluorescence emitted by living tissue, and an analysis device for analyzing obtained spectral images, such as measuring fluorescent wavelengths for living tissue diagnosis, and is also concerned with an image pickup unit in an industrial inspection device for obtaining spectral images of luminous surfaces such as those of LEDs and an analysis device for analyzing obtained spectral images, such as measuring spectroscopic properties of an object surface for quality control on a production line.
Devices in the prior art for measuring spectroscopic properties include those described in Japanese Laid Open Patent Application No. H02-104332 (which corresponds in subject matter to U.S. Pat. No. 5,078,150), in Japanese Laid Open Patent Application No. S63-271308, in U.S. Pat. No. 5,782,770, and in a document entitled “Spectral Camera” that was published on the Internet by DHT Corporation (found at: http://www.dht.co.jp/products/spectral camera/spectral camera.html).
Japanese Laid Open Patent Application No. H02-104332 discloses a spectroscopic endoscope in which illumination light is separated into multiple wave bands in a time-division manner via a rotating filter provided in the light source while continuously illuminating an object, thereby obtaining spectral images separated in a time-division manner.
Japanese Laid Open Patent Application No. S63-271308 discloses an endoscope having a variable transmittance element in the observation optical system wherein the wavelengths transmitted by the variable transmittance element may be successively changed, thereby enabling spectral images to be obtained for different wave bands.
U.S. Pat. No. 5,782,770 discloses a detection device in which a ribbon-shaped beam is used to illuminate an object, and spectral content of the image of the object is then detected via a dispersion element.
The Internet publication entitled “Spectral Camera” mentioned above discloses a spectral camera having a slit opening, a spectroscope, and a two-dimensional CCD camera in which light from an object is received via the slit opening and the light is then separated according to wavelength, thereby enabling the spectrum of an object to be obtained.
In the endoscopes for obtaining spectral images of an object described in Japanese Laid Open Patent Application Nos. H02-104332 and S63-271308 mentioned above, only object information carried by light of specific wavelength components from the object is imaged. For example, in a medical endoscope, only light of blue components reflected by the living tissue can be imaged to clearly depict the capillary blood vessels in the surface layer of the living tissue. In the endoscope described in Japanese Laid Open Patent Application No. S63-271308, a variable transmittance element is provided in the observation optical system. Thus, fluorescent images emitted by the object can be selectively obtained. However, it is difficult to obtain bands of smaller-wavelength separations using a rotating filter or a variable transmittance element. Therefore, high-resolution extraction of the spectrum of the object from obtained spectral images cannot be achieved.
On the other hand, with the devices for detecting the spectrum of an object described in U.S. Pat. No. 5,782,770, and in the document entitled “Spectral Camera” mentioned above, high resolution spectra can be obtained using a spectroscopic element. However, these devices do not provide color object images, making it impossible to examine the object while obtaining spectral information or to identify from which part of the object the spectral information is obtained. In order to obtain color images of an object using these devices, an image pickup optical system for obtaining color images must be additionally provided, or a mechanism for retracting the spectroscopic element from the optical path of the observation optical system must be provided, which alternatives are not desirable because this would require that the size of the device be increased.